Need help with Packard Bell 532 radio - UK Vintage Radio Repair and Restoration Discussion Forum

ct92404 · 3rd Jan 2017, 6:32 am

Hi everyone,

It's been about a year since I was last here! But I have another small table top AM vacuum tube radio I'm trying to restore. It's a Packard Bell model 532. I got it at an antique shop for cheap, I think around $5-$10, and it's just been sitting around for a couple of years. It was missing a couple of tubes, but when I installed them, the radio still wouldn't work. The tubes lit up but there was no sound whatsoever - no hum, no static, just nothing.

I found diagrams online, and I started taking measurements. I tested the DC voltage at the tubes (I think the "plate" voltage?) and it was very low. The schematic shows that the voltage at the 50C5 tube is supposed to be 105v from ground, but I was only getting around 5 volts! The DC voltage at the other tubes was low too, so I figured something must be going wrong at the 35w4 rectifier tube. I found a resistor that measured open, no continuity at all.

I got the diagrams from RadioMuseum.org, and I don't know what the rules are for posting copyrighted documents here. So I'll post a link to download the schematics instead, if anyone needs to see them:

http://www.radiomuseum.org/r/packard_be_532.html

The bad resistor is R10, which goes from pin 7 of the 35W4 tube to ground (via a capacitor). But the problem is that after I put a new resistor in, it started smoking and melting!

So there is obviously a short somewhere after the resistor. I think the problem might be with the capacitor - if it shorted, it would cause a direct path to ground, right? I see two capacitors in that area in the diagram, both are 50 mfd. Are those filter capacitors? And if one (or both) failed, can they cause a short circuit like that? I do have a Heathkit capacitor checker, but before I drag that thing out, I was just wondering if a capacitor can actually cause a short circuit if it fails? I have some experience with electrical circuits, but I'm still a bit new to fixing these antique radios. I admit I don't know exactly how they work.

Does anyone have any ideas? I know this is a UK site and maybe not too many people would be familiar with this radio, but I got good advice here last time! This is a really cool little radio, and I'd really like to get it working again.

- Chris

TonyDuell · 3rd Jan 2017, 6:54 am

This looks (at quick glance, I've not downloaded the schematic) to be a version of the well known AA5 ('All American 5') circuit. The added clock doesn't make much difference. (Incidentally posting Radiomuseum schematics here (which you have not done) is a bad idea, it can get you banned from the Radiomuesum site).

Now to answer some of your questions....

You'd call the high voltage on the tubes/valves the 'Plate voltage'. Over here we call it the 'Anode voltage'. And yes it comes from rectifying the mains with the 35W4. The 50uF capacitors are almost certainly the filter/smoothing capacitors and they do often fail shorted which would explain the overheating resistor. Before you get out your capacitor tester, just disconnect one end of each of the 50uF units and check them with an ohmmeter. They may show up as shorted like that.

Nuvistor · 3rd Jan 2017, 8:47 am

You may want to look at this web site, it describes the AA5 in detail, this page is the Power supply, just follow the links for the rest of the radio.

http://www.angelfire.com/electronic/...bes/AA5-1.html

Frank

ct92404 · 4th Jan 2017, 5:53 am

I got it! It's working now!

The filter capacitor did turn out to be the problem. It was a dual capacitor - two 50 microfarads capacitors in one, with a common negative. I disconnected it and put in another new resistor. Removing the capacitor seemed to eliminate the short circuit. The resistor didn't burn this time. So I bought two new electrolytic capacitors from an electronics shop, and installing them fixed the problem! The radio sounds pretty good!

I left it on for about an hour, and there was no signs of any other short circuits or other problems. Everything seemed to be working normally.

Thank you for your help guys! I learned a lot from this. This is now the second antique radio I've fixed and brought from completely non-working condition back to operation. It's feels so amazing to bring these antiques back to life!

- Chris

3rd Jan 2017, 6:32 am	#1
ct92404 Pentode Join Date: Sep 2015 Location: San Bernardino, California, USA. Posts: 101	Need help with Packard Bell 532 radio Hi everyone, It's been about a year since I was last here! But I have another small table top AM vacuum tube radio I'm trying to restore. It's a Packard Bell model 532. I got it at an antique shop for cheap, I think around $5-$10, and it's just been sitting around for a couple of years. It was missing a couple of tubes, but when I installed them, the radio still wouldn't work. The tubes lit up but there was no sound whatsoever - no hum, no static, just nothing. I found diagrams online, and I started taking measurements. I tested the DC voltage at the tubes (I think the "plate" voltage?) and it was very low. The schematic shows that the voltage at the 50C5 tube is supposed to be 105v from ground, but I was only getting around 5 volts! The DC voltage at the other tubes was low too, so I figured something must be going wrong at the 35w4 rectifier tube. I found a resistor that measured open, no continuity at all. I got the diagrams from RadioMuseum.org, and I don't know what the rules are for posting copyrighted documents here. So I'll post a link to download the schematics instead, if anyone needs to see them: http://www.radiomuseum.org/r/packard_be_532.html The bad resistor is R10, which goes from pin 7 of the 35W4 tube to ground (via a capacitor). But the problem is that after I put a new resistor in, it started smoking and melting! So there is obviously a short somewhere after the resistor. I think the problem might be with the capacitor - if it shorted, it would cause a direct path to ground, right? I see two capacitors in that area in the diagram, both are 50 mfd. Are those filter capacitors? And if one (or both) failed, can they cause a short circuit like that? I do have a Heathkit capacitor checker, but before I drag that thing out, I was just wondering if a capacitor can actually cause a short circuit if it fails? I have some experience with electrical circuits, but I'm still a bit new to fixing these antique radios. I admit I don't know exactly how they work. Does anyone have any ideas? I know this is a UK site and maybe not too many people would be familiar with this radio, but I got good advice here last time! This is a really cool little radio, and I'd really like to get it working again. - Chris

3rd Jan 2017, 6:54 am	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,213	Re: Need help with Packard Bell 532 radio This looks (at quick glance, I've not downloaded the schematic) to be a version of the well known AA5 ('All American 5') circuit. The added clock doesn't make much difference. (Incidentally posting Radiomuseum schematics here (which you have not done) is a bad idea, it can get you banned from the Radiomuesum site). Now to answer some of your questions.... You'd call the high voltage on the tubes/valves the 'Plate voltage'. Over here we call it the 'Anode voltage'. And yes it comes from rectifying the mains with the 35W4. The 50uF capacitors are almost certainly the filter/smoothing capacitors and they do often fail shorted which would explain the overheating resistor. Before you get out your capacitor tester, just disconnect one end of each of the 50uF units and check them with an ohmmeter. They may show up as shorted like that.

3rd Jan 2017, 8:47 am	#3
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Need help with Packard Bell 532 radio You may want to look at this web site, it describes the AA5 in detail, this page is the Power supply, just follow the links for the rest of the radio. http://www.angelfire.com/electronic/...bes/AA5-1.html Frank

4th Jan 2017, 5:53 am	#4
ct92404 Pentode Join Date: Sep 2015 Location: San Bernardino, California, USA. Posts: 101	Re: Need help with Packard Bell 532 radio I got it! It's working now! The filter capacitor did turn out to be the problem. It was a dual capacitor - two 50 microfarads capacitors in one, with a common negative. I disconnected it and put in another new resistor. Removing the capacitor seemed to eliminate the short circuit. The resistor didn't burn this time. So I bought two new electrolytic capacitors from an electronics shop, and installing them fixed the problem! The radio sounds pretty good! I left it on for about an hour, and there was no signs of any other short circuits or other problems. Everything seemed to be working normally. Thank you for your help guys! I learned a lot from this. This is now the second antique radio I've fixed and brought from completely non-working condition back to operation. It's feels so amazing to bring these antiques back to life! - Chris